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merlin el mago 8th December 2012 01:00 PM

The Morgan Jones mini tube headphone Amplifier
 
I want to build The Optimized Morgan Jones Amplifier but I have question about output cap beacuse I want to use film instead lytic: the schematic uses 470uF 350V, really is necessary so big or I can use a small film cap like 27uf or 10uF or less?

http://headwize.com/images4/cmoy5_1a.gif

jam 8th December 2012 02:25 PM

Too small a capacitor and you will have bass rolloff. Figure input impedance of headphones and calculate the rolloff with selected capacitor.

Jam

jam 8th December 2012 02:30 PM

1 Attachment(s)
First-order continuous-time implementation


Figure 1: A passive, analog, first-order high-pass filter, realized by an RC circuit
The simple first-order electronic high-pass filter shown in Figure 1 is implemented by placing an input voltage across the series combination of a capacitor and a resistor and using the voltage across the resistor as an output. The product of the resistance and capacitance (RC) is the time constant (τ); it is inversely proportional to the cutoff frequency fc, that is,


where fc is in hertz, τ is in seconds, R is in ohms, and C is in farads.

merlin el mago 8th December 2012 02:31 PM

I calculate 265uF for a load of 300 ohms (HD600), do you know if I can substitute the cathode resistor/capacitor with a 1.9-2.0-2.1V 20mA LED?

Stixx 8th December 2012 03:18 PM

1 Attachment(s)
Here you go... ;)

But when you want my opinion you'd better spend the money on output transformers than trying to pass the audio signal through humongous film capacitors.

kstagger 8th December 2012 03:23 PM

I once built a version of this amplifier - using a triode-connected EF86 on the front end, but with the same 6922 back-end - I did use electrolytics on the output, bypassed with Dayton polypropolenes. Really, it sounded quite good and certainly changed my mind about the "sound of electrolytics". If I remember correctly, I just used some Panasonics from Digikey.

merlin el mago 8th December 2012 03:27 PM

Thanks Stixx, I'm currently using the Valve Wizard mu-follower, I'm satisfied but I received advice that my Senhs HD600 plays better with an output impedance of 120 ohms, the mu-follower I'm using have an output impedance of 257 ohms so to big also I know HD600 have an output impedance of 300 ohms so the question is: wich value of SE output line transformer have I to install?, mu-follower schematic:

http://www.valvewizard.co.uk/Mufollower2.jpg

merlin el mago 8th December 2012 03:31 PM

Quote:

Originally Posted by kstagger (Post 3276200)
I once built a version of this amplifier - using a triode-connected EF86 on the front end, but with the same 6922 back-end - I did use electrolytics on the output, bypassed with Dayton polypropolenes. Really, it sounded quite good and certainly changed my mind about the "sound of electrolytics". If I remember correctly, I just used some Panasonics from Digikey.

I eard people used EF86 for MM phono preamp with great success.

DF96 8th December 2012 03:40 PM

A weakness of that MJ circuit is that it uses electrolytics to set the LF rolloffs. This is the most likely scenario to make electrolytic distortion a problem. Add an input coupling cap to set the LF rolloff, then ensure that the electrolytics are big enough to have very little signal voltage across them.

merlin el mago 8th December 2012 03:43 PM

Before the pot? Wich value?


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